The present invention relates to a heating element with a heating film having a support layer and a conductive layer. More particularly, the invention relates to a heating element comprising an electrically nonconductive support layer and a conductive layer deposited along and in contact with the nonconductive support layer wherein the support layer can be further defined as a flat product consisting of an electrically nonconductive material such as webs, woven fabrics, non-woven fabrics, and films having electrical connections. The present invention also relates to a heating element comprised of additional components such as upholstered units and/or sensors.
Traditional heating elements with heatable webs found in the prior art are generally comprised of graphite fibers. While these prior art heating elements utilizing graphite fibers generally exhibit good functionality and are advantageous in many circumstances, they generally require significant production costs and a large amount of capital investment for manufacture. The resulting high sale price of these heating elements having graphite fibers is often cost prohibitive and financially disadvantageous for a number of products and commercial applications fund in the marketplace.
In addition, heating elements and blankets utilizing an aluminum film as the heating film are also well known in the prior art. However, the use of aluminum film is often problematic in that it has a limited mechanical load capacity, and is therefore not suitable for a number of product applications. Further, a number of prior art devices have also attempted to utilize aluminum film wherein the aluminum film is laminated with a plastic film. However, these laminated versions of aluminum film are also limited due to mechanical load capacity.
Accordingly, there is a need for a low cost heating element and system that provides an electrically nonconductive support layer and a conductive layer, which has a large mechanical load capacity, can be employed across a wide range of different products and commercial applications, and which can be comprised of additional components such as upholstered units and/or sensors.
The present invention is directed to a heating element with a heating film having an electrically nonconductive support layer and a conductive layer deposited over and along the support layer wherein the conductive layer comprises a metallic material. The dual layer heating film of the present invention has the effect of increasing the mechanical load capacity of the heating element and reducing the cost of production and manufacture. In addition, the heating element of the present invention exhibits a high resistance to fire and reduces the potentiality of a short-circuit situation. In the event of an unintended short circuit at any location, the thin profile of the conductive layer may serve to facilitate a localized burn-off of the conductive layer. In this regard, an object of the present invention is to provide a heating element capable of reducing the effects of a short-circuit and achieve self-repair through localized burnoff of the conductive layer.
Though other materials are possible, it is contemplated that the support layer of the present invention will be comprised of plastic, in particular polyester, PI [polyimide], PA [polyamide], PP [polypropylene], or PC [polycarbonate], or of paper, and for the conductive layer to be applied or otherwise placed into contact with the support layer by means of vacuum evaporation, sputtering, or electroplating. This provides for sufficient resistance against various media such as perspiration or carbonated beverages, as well as UV light, and assures a low production cost. In addition, the present invention discloses a metallic conductive layer, which may be comprised, of copper or another suitable material having similar properties and that can be readily obtained at a low cost metal. It will also be appreciated to one of ordinary skill in the art that the conductive layer of the present invention could also be produced from aluminum, silver, gold, or nickel. Although various ranges, consistency, pattern, and thickness are possible, high stability and functionality are obtained especially when the thickness of the heating film lies between 10 and 300 xcexcm and, in particular, between 20 and 150 xcexcm, and the thickness of the conductive layer lies between 0.05 and 10 xcexcm and, in particular, between 0.05 and 1 xcexcm.
In order to assure reliable operation even under very heavy load, it is advisable for the ductility of the heating film to be relatively highxe2x80x94that is, higher than the ductility of a metallic film of the same thicknessxe2x80x94and for the conductive layer to be covered by a cover layer.
It is contemplated that the conductive layer of the heating film have at least one recess to form at least one conductive path, in order to guide the flow of current through said conductive layer in a targeted fashion. Furthermore, it is advantageous for at least one conductive path to have at least one slit, which serves to guide the flow of current through the conductive layer in a targeted fashion. This structuring allows the temperature distribution and power density in the heating film to be influenced. In this regard, when the current flows through a plurality of conductive paths and/or conductive strips, a concentration of current and resultant overheating at the interiors of bends can be avoided. At the same time, security of the heating element against failures is increased by the redundancy of conductive paths and/or conductive strips. For example, if the film disclosed in the present invention is used in the seating surface of a vehicle seat, the film does not wrinkle, but rather folds alongside the slits in a controlled fashion. This function results in improved seating comfort. Still further, the film can be adjusted to higher load conditions without overextension by spreading or spacing apart the slits. Similarly, the recesses and slits allow moisture to pass through the film, which assists, in providing comfort and air conditioning of the seating surface.
In order to uniformly distribute the current in the heating film, it is contemplated that at least two conductive strips be utilized which have approximately the same overall length. If a plurality of conductive paths are used in a particular application, it is preferred that at least two conductive paths have approximately the same overall length.
To improve the load capacity of the heating film, it is useful to have the slits or recesses, including a plurality of slits or recesses, running perpendicular to the directions of mechanical extension load.
In order to locally adjust the power per surface area and thus the temperature distribution, it is advisable to vary the width and/or thickness of least one conductive strip or one conductive path over the length of said conductive strip or conductive path. In this manner, areas with higher or lower temperatures may be adjusted in a targeted fashion.
In one embodiment, the heating film can be integrated into the seating surface and/or backrest surface of a vehicle seat. The film is well suited to these uses owing to its ease of processing.
In a particular non-limiting embodiment, the present invention discloses at least one slit, at least one connection point having at least two, but preferably a plurality, of adjacently disposed conductive strips electrically connected with one another at areas spaced from their respective ends, and at which the connected conductive strips would exhibit essentially the same potential, even without an electrical connection, during operation of the heating element. This increases the mechanical load capacity and manageability of the heating element.
In order to increase the functionality of the heating element, it is advantageous if at least a portion of the conductive layer does not serve, or does not serve exclusively, for heating, but rather serves additional electrical functional elements of the power supply, especially sensors.
It is advisable that the support layer and the cover layer be integrally joined to one another at the boundaries of at least one slit or one recess thereby reducing the possibility of corrosion of the conductive layer. For this same reason, it is useful if the support layer and/or the cover layer also completely overlap at least one slit or one recess.